I understood what you meant. I am beginning to think that umpty is an old-fashioned word that is not used much anymore, which is sad because it is a good word.
I grew up reading old books, so I have a funny vocabulary sometimes.
Of interest to wordy people, I probably should have used “umpteen”:
https://english.stackexchange.com/questions/114976/does-the-word-umpty-have-two-different-meanings
Both Merriam-Webster online dictionary and Readers English Japanese Dictionary at hand define ‘umpty’ as ‘such and such,’ in the same wording with an example, ‘umpty percent of all new houses’ in Merriam Webster. It sounds like simply saying ‘a certain’ or ‘X’ against an unidentifiable number or thing.
While both ‘Free dictionary’ and ‘Dictionary com’ define it as ‘an indefinite, fairly large number’ in the same wording.
snip
In America we no longer use the term umpty. We do, however, use the term umpteen (or perhaps umpsteen) See dictionary.reference.com/browse/umpteen?s=t. It means simply an indefinite, but large, number.